The overabundance of body hair (hirsutism) is caused by many factors, mainly genetic and hormonal, but it can also be caused by chemicals and medicines, such as minoxidil. Erkkola R, “Hirsutism: definitions and etiology” Ann Med., 22(2):99-103 (1990). The male hormone testosterone plays a pivotal role in hormonal hirsutism as its effect on body hair is to thicken and melanize (pigment) the hair. Paradoxically, the same hormone causes an opposite effect on scalp hair, provoking androgenetic alopecia (male pattern baldness), and the two phenotypes are commonly associated. This effect is not visible before puberty and, though seen mostly in males, also affects girls. In modern society there is no biological need for body hair, except for sexual aesthetics in males. In females, though, body hair is almost always seen as unpleasant and its presence can cause distress in affected women, who generally prefer smooth bodies. Moreover, even in males the presence of excessive body hair or its localization in particular areas (back, shoulders) is unwanted and there is a growing market pressure for methods to remove them.
Hair removal has a very long history. Scott et al., “Epilation,” Cutis, 46(3), 216-217 (1990). In ancient times all sorts of fanciful methods were used for the purpose, including tweezing and shaving with shells and pumice stones, sugaring, waxing and dissolution of the hair with caustic substances. Most of those treatments were painful and unsafe for the skin; moreover, they caused no permanent disappearance of the hair which instead grew back after varying periods. However, achieving permanent hair removal is much more difficult and only recently have permanent hair removal methods been developed.
Hair removal by chemical means is an established procedure but the effect is always temporary as no currently available chemical formulation is capable of penetrating deep into the hair follicle and reach the hair regenerative compartment, called the dermal papilla. Therefore, efficacy is limited to the hair shaft itself which is quickly regenerated by the papilla.
This is because of the hair follicle structure. FIG. 1. Every hair follicle comprises a dark, elongating column of cornified dead cells called the hair shaft. This is the visible hair and extends from the bulb to above the skin. At the base of the shaft lies a proliferating bulb which consists of a matrix of actively proliferating keratinocytes, which produce the hair shaft, surrounding a pine cone shaped organ made of mesenchimal (dermal) cells called the dermal papilla. This organ centralizes control of hair growth. It provides the matrix with the chemical signals to proliferate thus causing hair growth. At the same time it governs the hair growth cycle, which is typical of all hair. FIG. 2.
Every hair undergoes a growth phase called anagen, followed by a shedding phase called telogen, at the end of which the hair falls out and a new matrix is summoned by the dermal papilla to produce a new shaft. Bowden, et al., “Characterization and chromosomal localization of human hair-specific keratin genes and comparative expression during the hair growth cycle,” J. Invest Dermatol., 110(2), 158-164 (1998). This cycle continues throughout life and it is not influenced by shaving, because the external portion of the hair shaft is made of dead tissue and cannot communicate any information to the bulb. Every time a hair is plucked the traumatic event causes loss of the whole matrix and hair shaft but the dermal papilla is almost always left behind; if it weren't so tweezing would be permanent. The dermal papilla then restarts hair production just as if the hair had fallen out on its own. This is why all hair removal methods that act on the hair shaft are temporary. Only by inactivating the dermal papilla can permanent hair removal be achieved.
Current hair removal methods can be classified in two categories: methods which target the hair shaft (e.g., shaving, tweezing, waxing, sugaring) and methods which try to target the hair dermal papilla (e.g., electrolysis and laser treatment). The former are easy to implement but can only provide temporary effect. Targeting the dermal papilla is a much more complicated task because it lies deep in the dermis and it cannot be removed by mechanical means. It is very difficult to damage it without causing skin damage at the same time. Only recently have two technologies come about able to effectively target this organelle.
Hair electrolysis was first described in 1875 by a physician called Charles E. Michels. The technique involves inserting a fine metal conductor down into the hair shaft. An electric current is then applied and the hair bulb destroyed either by overheating (thermal electrolysis) or by the electrochemical local generation of caustic compounds (galvanic electrolysis). Because the hair bulb is targeted, the technique provides permanent hair removal. The main drawbacks of electrolysis are its slow rate (only one follicle can be treated per application), its painfulness, and the risk of scarring if sufficient care is not exerted. Nevertheless, electrolysis is now very popular throughout the world.
The most modern method available for permanent hair removal is performed using a laser. Mandt et al., “Epilation today: Physiology of the hair follicle and clinical photo-epilation,” J. Investig Dermatol Symp Proc., 10(3), 271-274 (2005). This technique was first discovered accidentally in the late 1970's and has since developed into the most popular technology on the market. Laser hair removal works by applying intense pulses of laser light at a certain wavelength on the hair after it has been shaven off. The principle is that, being the hair shaft of a different color than the rest of the skin, it will absorb more of the laser radiation. This results in the overheating of the shaft itself which will transmit this heat on to the dermal papilla, damaging it.
This method is effective, although not perfect, and it does reduce the coarseness of most hair. However, it also comes with drawbacks. Because of its principle of action, it works best where there is a strong color contrast between hair and surrounding skin, i.e. ideally black hair on white skin. When this is not the case, such as for light hair or dark complexions, the method is way less effective and can cause skin damage. It does instead often cause irritation. It is also expensive because of the equipment involved and must be carried out in specialized salons. Finally, because of its unpredictable efficiency, it cannot be considered a “permanent hair removal” but a “permanent hair reduction” method and it is so advertised.
PCT publication WO 01/80816 discloses the application of a topical composition for the permanent extinction of unwanted hair-growth. However, the composition is water based, and contains an enzyme, diluter (liquid), activator (of the enzyme), and an acid. The enzyme can be selected from oxidoreductases, preferably peroxidases.
Because there are few choices as to non-invasive methods for hair removal, permanent hair removal products are needed that are easily applied to the skin and effectively reduce the regrowth of hair.